This invention relates to a substrate holder for a chemical mechanical planarization (CMP) apparatus. More particularly, the present invention relates to a low friction, gimbaled wafer holder assembly for the planarization of substrates such as semiconductor wafers.
In a CMP apparatus, a substrate holder is typically used to hold a semiconductor wafer against a polishing pad during planarization. Certain known wafer holder assemblies use a ball joint so that the wafer holder can gimbal about a point during planarization. One such wafer holder assembly is disclosed in U.S. Pat. No. 5,593,344, hereby incorporated by reference in its entirety.
In one known ball joint wafer holder assembly, the wafer holder has a support frame that defines a hemispherical recess and a wafer chuck that comprises a hemispherical surface received within the hemispherical recess. Together, these two surfaces form a ball joint. One or both of the hemispherical surface and the hemispherical recess may have a fluid inlet connected to a source of fluid at a higher pressure, a fluid outlet connected to a fluid drain, and a bearing surface over which fluid flows from the source to the drain. The hemispherical surface is supported by the fluid over the bearing surface for rotation with respect to the support about a center of rotation during planarization.
Wafer holder assemblies employing ball joints may experience a performance degradation due to a friction force from the hemispherical surface of the wafer chuck rubbing against the hemispherical recess of the support frame during planarization. Accordingly, there is a need to develop a substrate holder assembly that experiences less friction than a ball joint-containing assembly during planarization.
In one aspect of the invention, an assembly for holding a substrate in a CMP apparatus is provided. The assembly comprises a holder frame insertable into the CMP apparatus, the holder frame having an inner wall. They assembly also includes at least one rolling mechanism rotatably mounted in the holder frame such that at least a portion of the rolling mechanism protrudes from the inner wall. The assembly further comprises a wafer chuck movably mounted in the holder frame, the wafer chuck having a first side shaped to substantially conform to the inner wall and to be in continuous contact with the at least one rolling mechanism during planarization, and a second side adapted to receive a substrate for planarization.
In another aspect of the invention, an assembly for holding a substrate in a CMP apparatus comprises a holder frame insertable into the CMP apparatus, the holder frame having an inner wall, the inner wall defining a substantially hemispherical recess. The assembly further includes a plurality of rolling mechanisms rotatably mounted in the holder frame such that at least a portion of each rolling mechanism protrudes from the inner wall. The assembly also includes a wafer chuck movably mounted in the holder frame, the wafer chuck having a first side shaped to substantially hemispherically and the first side being adapted to be in continuous contact each of the plurality of rolling mechanisms during planarization, and a second side adapted to receive a semiconductor wafer for planarization.
In yet another aspect of the invention, an improved wafer holder in a CMP apparatus is provided. The improvement comprises a gimbaling mechanism in the holder that permits gimbaling of a wafer chuck in a wafer holder frame during planarization substantially without a friction force caused by the wafer chuck rubbing against an inner wall of the wafer holder frame by providing at least one rolling mechanism rotatably mounted with the inner wall and protruding at least partially therefrom, wherein the wafer chuck contacts the rolling mechanism as the wafer chuck gimbals during planarization.
In still another aspect of the invention, a method of reducing friction in a gimbaling mechanism of a wafer chuck in a wafer holder in a CMP apparatus during planarization is provided. The method comprises (a) providing a wafer holder frame with an inner wall, the inner wall having at least one rolling mechanism rotatably mounted thereon, the rolling mechanism at least partially protruding from the inner wall; (b) movably mounting a wafer chuck in the wafer holder frame, the wafer chuck having a first side adapted to contact the at least one rolling mechanism and a second side adapted to receive a substrate for planarization; and (c) contacting the first side of the wafer chuck with the at least one rolling mechanism to provide gimbaling motion during planarization, thereby reducing the friction force cause by contacting the first side of the wafer chuck with the inner wall of the wafer holder.
The present invention provides the foregoing and other features, and the advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention and do not limit the scope of the invention, which is defined by the appended claims and equivalents thereof.